In a bent axis type axial piston pump/motor, for example, a shaft center of a cylinder block is arranged in an inclined state with respect to a drive shaft, which is rotatably supported by a casing, as described in Patent Literature 1. A center shaft and a plurality of piston rods are arranged on one end face facing the drive shaft in the cylinder block. The center shaft is arranged at a position on the shaft center of the cylinder block, and the plurality of piston rods are arranged at equal intervals on a circumference having the center shaft as the center. A supporting end, which projects out from one end face of the cylinder block in the center shaft, and a supporting end, which projects out from one end face of the cylinder block in the piston rod, are each configured to have a spherical shape and are supported in a tiltable manner on one end face of the drive shaft.
A valve plate for rotatably supporting the cylinder block is brought into contact with the other end face of the cylinder block. The valve plate includes a high pressure port and a low pressure port, which are selectively connected to a cylinder bore according to the rotation position of the cylinder block.
In the bent axis type axial piston pump/motor configured as above, the piston rod moves a stroke in the cylinder bore according to the tilt angles of the drive shaft and the cylinder block when the drive shaft and the cylinder block are rotated around the shaft centers respectively. Therefore, for example, if oil is supplied to the high pressure port and the low pressure port is connected to an oil tank, the piston rods advance and move in turn in the cylinder bore connected to the high pressure port and the piston rods degenerate and move in turn in the cylinder bore connected to the low pressure port, so that the cylinder block is rotated and the desired rotation force is obtained through the drive shaft.
In this type of bent axis type axial piston pump/motor, a push spring is generally interposed between the center shaft and the cylinder block. The push spring prevents leakage caused when the oil passes between the high pressure port of the valve plate and the cylinder bore by pushing the other end face of the cylinder block against the valve plate. Therefore, the leakage of oil is reliably prevented by applying the push spring having a large attachment load. For instance, Patent Literature 1 describes applying the push spring having a large attachment load if a shaft portion of the center shaft is configured to have a thick diameter, thus reliably preventing the oil leakage from between the valve plate and the cylinder block to enhance the volume efficiency of the motor.